feat(spark): deploy persistent Spark cluster with Web UI

- Add spark-cluster/base with Bitnami Spark chart 9.2.10 (master +
  2 workers), spark-events PVC (RWO/local-path), and Ingress resources
  for spark.nowchess.janis-eccarius.de (master UI) and
  spark-history.nowchess.janis-eccarius.de (history placeholder)
- Add spark-cluster/eu-central-1-prod overlay and ArgoCD Application
  (automated prune + selfHeal)
- Migrate all spark-analytics CronJobs and streaming Deployment from
  K8s-native mode (k8s://...) to Spark standalone (spark://spark-master:7077);
  drop kubernetes-specific --conf flags; add eventLog confs; mount
  spark-events PVC on all job pods

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

eu-central-1/argo-apps/spark-cluster/spark-cluster.yaml

@@ -0,0 +1,18 @@
+apiVersion: argoproj.io/v1alpha1
+kind: Application
+metadata:
+  name: spark-cluster
+  namespace: argocd
+spec:
+  project: default
+  destination:
+    namespace: nowchess
+    server: https://kubernetes.default.svc
+  sources:
+    - repoURL: git@git.janis-eccarius.de:NowChess/Gitops.git
+      path: ./spark-cluster/eu-central-1-prod
+      targetRevision: main
+  syncPolicy:
+    automated:
+      prune: true
+      selfHeal: true